Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.
Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft mounted on a base plate and a hub, to which the spindle is attached, having a sleeve into which the shaft is inserted. Permanent magnets attached to the hub interact with a stator winding on the base plate to rotate the hub relative to the shaft. In order to facilitate rotation, one or more bearings are usually disposed between the hub and the shaft.
Over the years, storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage disks. The bearing assembly that supports the storage disk is of critical importance. One bearing design is a fluid dynamic bearing. In a fluid dynamic bearing, a lubricating fluid such as air or liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disk hub. In addition to air, typical lubricants include gas, oil, or other fluids. Fluid dynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface reduces wobble or run-out between the rotating and fixed members. Further, the use of fluid in the interface area imparts damping effects to the bearing, which helps to reduce non-repeat run-out. Thus, fluid dynamic bearings are an advantageous bearing system.
However, as the size, height, and power consumption of fluid dynamic bearing motors is decreased, several problems become more prominent. For one, reducing the size of the motor features, which is a preferred approach to reducing power consumption, tends to alter the geometry of the features in such a way that comprises their structural integrity. A reduction in the diameter of the shaft forces a reduction in the size of the disc clamping screw, or a reduction in wall thickness in the shaft surrounding the screw. This can result in compromises in structural integrity. For another, as the motors themselves become shorter in height, the spacing between bearing components decreases, minimizing the angular or rocking stiffness of the bearings. Also, the power consumed by the bearings, especially at low temperatures, limits the power available to other motor components. As rotational speed increases, this problem worsens.
Therefore, a need exists for a fluid dynamic bearing design that accommodates current size, height, and power consumption demands without compromising the structural integrity or functionality of the bearings and other motor components.